In a conventional constriction machine, a portion of work equipment such as a cylinder is typically driven by a hydraulic fluid. Consequently, the construction machine is provided with a hydraulic circuit for driving the cylinder or the like. The hydraulic circuit is provided with, for example, a hydraulic tank and a pump for pumping the hydraulic fluid from the hydraulic tank. In addition, the hydraulic circuit is sometimes provided with a bubble removing device for removing bubbles in the hydraulic fluid because bubbles generated in the hydraulic circuit may damage the pump. Since demands for size reduction of components equipped on construction machines have been on the rise, a lot of construction machines are provided with a bubble removing device in a hydraulic tank in recent years.
The hydraulic fluid from which bubbles have been removed by the bubble removing device in the hydraulic tank flows out through an outflow port of the bubble removing device to the hydraulic fluid in the tank. The hydraulic fluid is fed out through a delivery port of the tank, and then, is pumped back to the hydraulic circuit by the pump. The bubbles removed by the bubble removing device are discharged to the hydraulic fluid in the tank through a bubble exhaust port provided on the bubble removing device independently of the outflow port. With this arrangement, since the bubble exhaust port of the bubble removing device and the delivery port of the hydraulic tank are closely disposed on account of the size reduction of the hydraulic tank, the hydraulic fluid containing the bubbles discharged from the bubble exhaust port may unfavorably be fed out from the delivery port together with the hydraulic fluid from which the bubbles have been removed.
To prevent this problem, a hydraulic tank including a guide portion that separates a side of the outflow port for the hydraulic fluid from which the bubbles have been removed and the delivery port of the tank from a side of the bubble exhaust port for the bubbles and guides the hydraulic fluid to the delivery port, the hydraulic fluid being substantially limited to the fluid that comes out from the outflow port, has been known (e.g., Patent Document 1).
Another tank has been known which includes a complex bubble removing device formed by covering with a closure plate a whole of several juxtaposed bubble removing devices, the complex bubble removing device being connected to the delivery port of the tank by a return pipe (e.g., Patent Document 2).
Furthermore, another tank is known which includes an inner chamber connecting a return port for the hydraulic fluid in an upper portion of the tank and a delivery port in a lower portion of the tank, the inner chamber housing a spiral baffle, the baffle being provided with a hollow shaft along a central axis of the baffle, the hollow shaft being provided with ventilation holes on a circumferential wall of the hollow shaft (e.g., Patent Document 3). In the tank disclosed in Patent Document 3, flow of the hydraulic fluid on the spiral baffle in the inner chamber generates a swirl, so that hydraulic fluid containing bubbles that are drawn to the central portion of the inner chamber is discharged through the hollow shaft in the central portion of the inner chamber to the outside of the tank.
Patent Document 1: JP-A-2004-84923
Patent Document 2: JP-A-08-318103 (FIGS. 9 and 10)
Patent Document 3: U.S. Pat. No. 2,316,729